KR20230076258A - Method and apparatus for security settings in communication system - Google Patents

Abstract

A security setting technique in a communication system is disclosed. An operating method performed in a current serving base station of a communication system, comprising: receiving a radio resource control (RRC) request message from a terminal; Requesting context recovery to a previous serving base station when identification of the terminal fails; Receiving context information about the terminal and security algorithm information set with the terminal from the previous serving base station; and transmitting an RRC response message including security algorithm information in use to the terminal when the security algorithm according to the security algorithm information is different from the security algorithm in use. It can be.

Description

Security setting method and device in communication system {METHOD AND APPARATUS FOR SECURITY SETTINGS IN COMMUNICATION SYSTEM}

The present invention relates to a security setting technology in a communication system, and more particularly, to a security setting technology in a communication system enabling security to be set in a process of recovering a terminal context.

Along with the development of information and communication technology, various wireless communication technologies may be developed. Representative wireless communication technologies may include long term evolution (LTE) and new radio (NR), which are defined in the 3rd generation partnership project (3GPP) standard. LTE may be one wireless communication technology among 4th generation (4G) wireless communication technologies, and NR may be one wireless communication technology among 5th generation (5G) wireless communication technologies.

For the processing of rapidly increasing wireless data after the commercialization of 4G communication systems (eg, communication systems supporting LTE), the frequency band (eg, frequency bands below 6 GHz) of the 4G communication system as well as the 4G communication system A 5G communication system (eg, a communication system supporting NR) using a frequency band higher than the frequency band of (eg, a frequency band of 6 GHz or higher) may be considered. The 5G communication system may support eMBB (enhanced Mobile BroadBand), URLLC (Ultra-Reliable and Low Latency Communication), and mMTC (massive machine type communication).

In such a communication system, a terminal and a base station may perform a radio resource control (RRC) reestablishment procedure and an RRC resume procedure as needed. The RRC re-establishment procedure and the RRC resume procedure may be performed by the UE for a new base station when the UE moves or there is a change in the radio environment. In this situation, a new base station that has received an RRC message from a terminal may be unable to determine whether the corresponding terminal is a terminal previously connected to itself.

At this time, the new base station may proceed with a context retrieve procedure of the terminal in order to check whether the terminal requesting RRC re-establishment or RRC resumption is a terminal that has previously accessed the base station. In such a terminal context recovery procedure, security settings between the base station and the terminal can play a very important role in the process of identifying the terminal and verifying the validity of the message. In this regard, according to the current 3GPP standard, security settings between a new base station and a terminal may not match when performing an RRC re-establishment procedure or an RRC resume procedure including a terminal context recovery procedure.

An object of the present invention to solve the above problems is to provide a security setting method and apparatus in a communication system that allows a terminal and a base station to set security that matches in the process of recovering the context of the terminal.

To achieve the above object, a security setting method in a communication system according to a first embodiment of the present invention is an operation method performed in a current serving base station of the communication system, comprising the steps of receiving a radio resource control (RRC) request message from a terminal. ; Requesting context recovery to a previous serving base station when identification of the terminal fails; Receiving context information about the terminal and security algorithm information set with the terminal from the previous serving base station; and transmitting an RRC response message including security algorithm information in use to the terminal when the security algorithm according to the security algorithm information is different from the security algorithm in use. It can be.

According to the present application, when a previous serving base station receives a request for context recovery of a terminal from a current serving base station, security algorithm information being used by the terminal and security settings may be provided to the current serving base station. Accordingly, when the current serving base station cannot support the security algorithm used by the previous serving base station and uses a new security algorithm, new security algorithm information can be provided to the terminal.

As a result, when the current serving base station performs a procedure for restoring the context of the terminal, it is possible to solve the problem of inconsistency in security settings between the terminal and the base station. That is, when the current serving base station performs an RRC re-establishment procedure or an RRC resume procedure including context recovery of the terminal, it is possible to solve a problem in which security settings between the current serving base station and the terminal do not match.

In addition, according to the present application, when the terminal moves out of the communication area of the previous serving base station and moves to the communication area of the new base station by movement, the RRC re-establishment procedure or RRC resumes when the security algorithm of the previous serving base station and the new base station are different. The procedure can proceed successfully.

1 is a conceptual diagram illustrating a first embodiment of a communication system.
2 is a block diagram showing a first embodiment of a communication node constituting a communication system.
3 is a flowchart illustrating a first embodiment of a method for setting security between a terminal and a base station.
4 is a flowchart illustrating a first embodiment of a method for resuming radio resource control (RRC).
5 is a flowchart illustrating a first embodiment of an RRC re-establishment method.
6 is a conceptual diagram for explaining a change in a transmission target of an RRC message according to movement of a terminal.
7 is a flowchart illustrating a first embodiment of a method for restoring a context of a terminal.
8 is a flowchart illustrating a second embodiment of a method for restoring a context of a terminal.

Since the present invention can make various changes and have various embodiments, specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. The terms and/or include any combination of a plurality of related recited items or any of a plurality of related recited items.

In embodiments of the present application, “at least one of A and B” may mean “at least one of A or B” or “at least one of combinations of one or more of A and B”. Also, in the embodiments of the present application, “one or more of A and B” may mean “one or more of A or B” or “one or more of combinations of one or more of A and B”.

It is understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may exist in the middle. It should be. On the other hand, when an element is referred to as “directly connected” or “directly connected” to another element, it should be understood that no other element exists in the middle.

Terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in this application, they should not be interpreted in an ideal or excessively formal meaning. don't

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail. In order to facilitate overall understanding in the description of the present invention, the same reference numerals are used for the same components in the drawings, and redundant descriptions of the same components are omitted.

1 is a conceptual diagram illustrating a first embodiment of a communication system.

Referring to FIG. 1, a communication system 100 includes a plurality of communication nodes 110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6). Here, the communication system may be referred to as a “communication network”. Each of the plurality of communication nodes may support at least one communication protocol. For example, each of the plurality of communication nodes is a communication protocol based on code division multiple access (CDMA), a communication protocol based on wideband CDMA (WCDMA), a communication protocol based on time division multiple access (TDMA), and a frequency division multiple (FDMA) access) based communication protocol, OFDM (orthogonal frequency division multiplexing) based communication protocol, OFDMA (orthogonal frequency division multiple access) based communication protocol, SC (single carrier)-FDMA based communication protocol, NOMA (non-orthogonal multiple access) access)-based communication protocol, space division multiple access (SDMA)-based communication protocol, and the like may be supported. Each of the plurality of communication nodes may have the following structure.

2 is a block diagram showing a first embodiment of a communication node constituting a communication system.

Referring to FIG. 2 , a communication node 200 may include at least one processor 210, a memory 220, and a transceiver 230 connected to a network to perform communication. In addition, the communication node 200 may further include an input interface device 240, an output interface device 250, a storage device 260, and the like. Each component included in the communication node 200 may be connected by a bus 270 to communicate with each other. However, each component included in the communication node 200 may be connected through an individual interface or an individual bus centered on the processor 210 instead of the common bus 270 . For example, the processor 210 may be connected to at least one of the memory 220, the transmission/reception device 230, the input interface device 240, the output interface device 250, and the storage device 260 through a dedicated interface. .

The processor 210 may execute a program command stored in at least one of the memory 220 and the storage device 260 . The processor 210 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present invention are performed. Each of the memory 220 and the storage device 260 may include at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 220 may include at least one of a read only memory (ROM) and a random access memory (RAM).

Referring back to FIG. 1, the communication system 100 includes a plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2), a plurality of user equipment (UEs). ) (130-1, 130-2, 130-3, 130-4, 130-5, 130-6). Each of the first base station 110-1, the second base station 110-2, and the third base station 110-3 may form a macro cell. Each of the fourth base station 120-1 and the fifth base station 120-2 may form a small cell. The fourth base station 120-1, the third UE 130-3, and the fourth UE 130-4 may belong to the coverage of the first base station 110-1. The second UE 130-2, the fourth UE 130-4, and the fifth UE 130-5 may belong within the coverage of the second base station 110-2. The fifth base station 120-2, the fourth UE 130-4, the fifth UE 130-5, and the sixth UE 130-6 may belong within the coverage of the third base station 110-3. . The first UE 130-1 may belong within the coverage of the fourth base station 120-1. The sixth UE 130-6 may belong within the coverage of the fifth base station 120-2.

Here, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 is a NodeB, an evolved NodeB, a base transceiver station (BTS), radio base station, radio transceiver, access point, access node, roadside unit (RSU), digital unit (DU), cloud digital unit (CDU) , a radio remote head (RRH), a radio unit (RU), a transmission point (TP), a transmission and reception point (TRP), a relay node, and the like. Each of the plurality of UEs 130-1, 130-2, 130-3, 130-4, 130-5, and 130-6 includes a terminal, an access terminal, a mobile terminal, It may be referred to as a station, subscriber station, mobile station, portable subscriber station, node, device, and the like.

A plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6) Each may support cellular communication (eg, long term evolution (LTE), advanced (LTE-A), etc. specified in the 3rd generation partnership project (3GPP) standard). Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may operate in different frequency bands or may operate in the same frequency band. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to each other through ideal backhaul or non-ideal backhaul, and ideal backhaul Alternatively, information can be exchanged with each other through non-ideal backhaul. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to a core network (not shown) through an ideal backhaul or a non-ideal backhaul. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits a signal received from the core network to a corresponding UE 130-1, 130-2, 130-3, and 130. -4, 130-5, 130-6), and the signal received from the corresponding UE (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) to the core network can be sent to

Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may support OFDMA-based downlink transmission, and may support SC-FDMA-based uplink transmission. ) can support transmission. In addition, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits multiple input multiple output (MIMO) (eg, single user (SU)-MIMO, MU (multi user)-MIMO, massive MIMO, etc.), CoMP (coordinated multipoint) transmission, carrier aggregation transmission, transmission in unlicensed band, device to device (D2D) ) communication (or proximity services (ProSe)), etc. Here, each of the plurality of UEs 130-1, 130-2, 130-3, 130-4, 130-5, and 130-6 is a base station Operations corresponding to (110-1, 110-2, 110-3, 120-1, 120-2) supported by base stations 110-1, 110-2, 110-3, 120-1, 120-2 action can be performed.

In such a communication system, a terminal and a base station may perform a radio resource control (RRC) reestablishment procedure and an RRC resume procedure as needed. Here, both the RRC re-establishment procedure and the RRC resume procedure may be procedures that may occur after the UE accesses the base station. The RRC re-establishment procedure may occur when a terminal connected to the base station fails in handover (HO), when a problem occurs in a radio section, or when there is a logical problem in setting a specific parameter instructed by the base station. The RRC resumption procedure may be a procedure initiated by the terminal to reconnect when the connection with the base station is released. Such an RRC resumption procedure may have the advantage of simplifying the message procedure until accessing the base station compared to the existing RRC setup procedure.

The RRC re-establishment procedure and the RRC resumption procedure may proceed with respect to the base station to which the terminal was connected. In addition, the RRC re-establishment procedure and the RRC resume procedure may be performed by the UE for a new base station when the UE moves or there is a change in the radio environment. When a terminal performs an RRC re-establishment procedure or an RRC resume procedure with a new base station, the new base station receiving a message from the terminal may be unable to determine whether the corresponding terminal is a terminal previously connected to itself. At this time, the new base station may proceed with a context retrieve procedure of the terminal in order to check whether the terminal requesting RRC re-establishment or RRC resumption is a terminal that has previously accessed the base station.

As such, the context recovery procedure of the terminal is a procedure for requesting identification of the terminal from a neighboring base station that is determined to have previously accessed the terminal when the base station receiving the RRC re-establishment or RRC resume request from the terminal does not identify the corresponding terminal. can The base station may proceed with a normal RRC re-establishment procedure and an RRC resumption procedure when the context recovery of the UE is successful. In this way, security settings between the base station and the terminal in the context recovery procedure of the terminal can play a very important role in the process of identifying the terminal and verifying the validity of the message. Consistent security settings between the terminal and the base station may be essential for performing the RRC re-establishment procedure and the RRC resume procedure. According to the current 3GPP standard, security settings between a new base station and a terminal may not match when performing an RRC re-establishment procedure or an RRC resume procedure including a context recovery procedure of a terminal.

Meanwhile, such a mobile communication system may use various algorithms for message integrity protection and encryption. Here, the integrity protection may be to protect the received message so that it is not changed from an external attack. And, encryption may be a function that makes interpretation impossible when the received message is exposed to a third party. Currently, representative security algorithms used in mobile communication systems may include SNOW3G, advanced encryption standard (AES), zeuxcoin (ZUC), and the like. Here, SNOW3G may be an algorithm based on a linear feedback shift register (LFSR) having 608 bits of state. And, AES may be a standard encryption used by the US government to protect confidential information on storage devices. Next, ZUC may be an official LTE 3rd generation encryption algorithm that passed the 3GPP general meeting held in September 2011 as a Chinese write encryption algorithm.

A general security-related setting procedure may be performed in the form of deriving a lower key from an upper key matched between two nodes through the same algorithm. Security setting between the terminal and the base station may be performed using a top key called Kgnb. The terminal and the base station may have identical Kgnb from the logic performed through each independent procedure. The terminal and the base station can derive four types of subkeys from Kgnb to be applied between the terminal and the base station as follows.

1) Krrc_int: Key to be applied to RRC message integrity protection

2) Krrc_enc: Key to be applied to RRC message encryption

3) Kup_int: Key to be applied to user data integrity protection

4) Kup_enc: Key to be applied to encrypt user data

Such subkeys of Kgnb can be derived from different input variables and Kgnb according to algorithms applied to integrity protection and encryption.

3 is a flowchart illustrating a first embodiment of a method for setting security between a terminal and a base station.

Referring to FIG. 3 , after determining an algorithm to be used for integrity protection and encryption, the base station may inform the terminal of integrity protection algorithm information and encryption algorithm information through a security mode command message (S310). And, the base station may instruct the terminal to use the determined security algorithm. At this time, the base station may derive Krrc_int, which is a lower key, from the determined integrity protection algorithm and Kgnb. Then, the base station may transmit a security mode command message to which integrity protection is applied to the terminal using the derived Krrc_int.

Meanwhile, the terminal may receive a security mode command message from the base station. At this time, the terminal may transmit a security mode complete message to the base station when integrity verification and internal setting of the received security mode command message are successful (S320). At this time, the terminal may derive Krrc_int, which is a lower key, from the corresponding indecision protection algorithm and Kgnb according to the integrity protection algorithm information received from the base station. In addition, the terminal may derive Krrc_enc, which is a lower key, from the corresponding encryption algorithm and Kgnb according to the encryption algorithm information received from the base station. And, the terminal may encrypt the security mode complete message using the derived Krrc_enc. Then, the terminal may transmit the security mode complete message to the base station after integrity protection using the derived Krrc_int.

Accordingly, the base station may receive a security mode complete message from the terminal. And, the base station can decode the received security mode complete message using Krrc_enc, and can verify indecision using Krrc_int.

Meanwhile, the RRC resume procedure may be a procedure in which a UE in an RRC inactive state transitions to an RRC connected state. In order for the terminal to reconnect to the base station in the RRC release state, a message procedure may have to be interlocked with an access and mobility management function (AMF), which is a core network. However, the RRC resume procedure may allow the base station to maintain the context of the terminal that has transitioned to the RRC inactive state. Accordingly, the RRC resume procedure is a relatively simplified message procedure between the terminal and the base station, and can transition the state of the terminal to the RRC connected state.

4 is a flowchart illustrating a first embodiment of a method for resuming radio resource control (RRC).

Referring to FIG. 4, the base station may transmit an RRC release message including information element (IE) suspend configuration to the terminal in order to transition the terminal in the connected state to the RRC inactive state. (S410). Accordingly, the terminal may receive an RRC release message from the base station. In addition, the terminal may transition to the RRC inactive state after storing the IE inactive network temporary identity (I-RNTI) in the IE reservation configuration information of the received RRC release message.

Thereafter, the terminal may transmit an RRC resume request message to the base station in order to transition from the RRC inactive state to the RRC connected state for various reasons (S420). At this time, the terminal may include the IE I-RNTI received through the RRC release message and the resume MAC-I (resume message authentication code-integrity) in the RRC resume request message and transmit it to the base station. Here, the terminal may generate the resume MAC-I using Krrc_int derived by an integrity protection algorithm previously set according to a terminal-base station security setting procedure when accessing a base station. The terminal may derive Kgnb* by updating Kgnb, and may derive a subkey from the derived Kgnb* through an integrity protection algorithm set during an existing connection.

Meanwhile, the base station receiving the RRC resume request message can identify the existing terminal from the resume MAC-I and I-RNTI included in the RRC resume request message (S430). When the base station succeeds in identifying the existing terminal, the context of the terminal may be restored. In addition, the base station may derive Kgnb* by updating Kgnb, and may derive a subkey from Kgnb* through an integrity protection algorithm set during an existing connection. The base station may transmit an RRC resume message to the identified terminal (S440).

At this time, the base station may protect the integrity of the RRC resume message through Krrc_int newly derived from Kgnb*. Meanwhile, the terminal may receive an RRC resume message from the base station. At this time, the terminal may verify the integrity of the RRC resume message through Krrc_int. Thereafter, the terminal may transmit an RRC resume completion message to the base station (S450). At this time, the terminal may integrity-protect the RRC resume complete message through Krrc_int and encrypt it through Krrc_enc. Thereafter, the terminal may end the procedure after transitioning the state from the RRC inactive state to the RRC connected state.

On the other hand, the RRC re-establishment procedure may be a procedure for recovering the problem when a terminal in an RRC connected state detects a problem in a radio section due to a specific reason.

5 is a flowchart illustrating a first embodiment of an RRC re-establishment method.

Referring to FIG. 5 , the terminal may maintain a connection state capable of transmitting and receiving data (S510). And, when the terminal detects a problem in the radio section, it can transmit an RRC reestablishment request message including an IE short MAC-I to the base station to recover it (S520). Here, the shortened MAC-I may be generated through Krrc_int set according to a security setting procedure between a terminal and a base station during an existing connection. The terminal may derive Kgnb* by updating Kgnb, and may derive a subkey from Kgnb* through an integrity protection algorithm set during an existing connection.

Meanwhile, the base station may receive an RRC re-establishment request message from the terminal, and may identify the existing terminal from the shortened MAC-I included in the received RRC re-establishment request message (S530). In addition, the base station may derive Kgnb* by updating Kgnb, and may derive a subkey from Kgnb* through an integrity protection algorithm set during an existing connection. Thereafter, the base station may transmit an RRC re-establishment message to the identified terminal (S540). The base station may protect the integrity of the RRC re-establishment message through Krrc_int newly derived from Kgnb*.

Meanwhile, the terminal may receive an RRC re-establishment message from the base station. The UE can verify the integrity of the RRC re-establishment message through Krrc_int. Thereafter, the terminal may transmit an RRC re-establishment completion message to the base station (S550). At this time, the terminal may integrity-protect the RRC re-establishment complete message through Krrc_int and encrypt it through Krrc_enc.

Meanwhile, the procedure specified in FIGS. 4 and 5 may be the case where the destination base station to which the terminal transmits the RRC re-establishment or RRC resume message is the same as the base station receiving the service. In this case, the base station can check which terminal is internally managed by the base station through a procedure for identifying the terminal, which transmits the RRC message. However, when the base station from which the terminal has received service and the destination base station to which the RRC re-establishment or RRC resume message is to be transmitted are different, the new base station may fail to restore the context of the terminal.

6 is a conceptual diagram for explaining a change in a transmission target of an RRC message according to movement of a terminal.

Referring to FIG. 6 , a terminal 610 in an RRC connected state or an RRC inactive state may move from a communication area of a previous serving base station 620-1 to a communication area of a current serving base station 620-2. At this time, the terminal 610 may transmit an RRC re-establishment request message or an RRC resume request message to the current serving base station 620-2 in order to access the current serving base station 620-2. Accordingly, the current serving base station 620 - 2 may receive an RRC re-establishment request message or an RRC resume request message from the terminal 610 .

At this time, the current serving base station 620 - 2 may attempt to identify which context among contexts being managed internally through a procedure for identifying a terminal. However, the current serving base station 620-2 may fail to recover the context of the terminal. In this case, the current serving base station 620-2 may request context recovery of the terminal to the previous serving base station 620-1.

7 is a flowchart illustrating a first embodiment of a method for restoring a context of a terminal.

Referring to FIG. 7 , in the context recovery method of the terminal, the terminal may move from the communication area of the previous serving base station to the communication area of the current serving base station. Accordingly, the terminal may transmit an RRC resume or RRC re-establishment request message to the current serving base station (S711). Then, the current serving base station may receive an RRC resume or RRC re-establishment request message from the terminal.

And, the current serving base station may attempt to identify which context among the contexts being managed internally through a procedure for identifying the terminal, but may fail to identify the terminal (S712). Accordingly, the current serving base station may fail to recover the context of the terminal. In this case, the current serving base station may transmit a context retrieve request message of the terminal including the resume MAC-I or shortened MAC-I to the previous serving base station (S713).

Accordingly, the previous serving base station may receive the context recovery request message of the terminal from the current serving base station. And, the previous serving base station can identify the existing terminal from the resume MAC-I or shortened MAC-I included in the context recovery request message of the received terminal (S714). Then, the previous serving base station may transmit a context retrieve response message of the terminal including the context of the terminal to the current serving base station (S715). At this time, the context recovery response message of the terminal may include the following parameters.

1) UE security capabilities: list of security-related algorithms supported by the UE

2) AS (autonomous system) security information: Kgnb derived from Kgnb*

Meanwhile, the current serving base station may receive the context recovery response message of the terminal from the previous serving base station. And, the current serving base station can restore the context of the terminal based on the context information of the terminal in the context recovery response message of the terminal received from the previous serving base station. In addition, the current serving base station may derive Kgnb* by updating Kgnb, and may derive a subkey Krrc_int from Kgnb* through an integrity protection algorithm. Thereafter, the current serving base station may transmit an RRC resume or RRC re-establishment message to the terminal (S716). The current serving base station can protect the integrity of the RRC resume or RRC re-establishment message through Krrc_int newly derived from Kgnb*.

Meanwhile, the terminal may receive an RRC resume or RRC re-establishment message from the current serving base station. The terminal may derive Kgnb* by updating Kgnb, and may verify the integrity of the RRC resume or RRC re-establishment message through Krrc_int derived from Kgnb*. Thereafter, the terminal may transmit an RRC resume or RRC re-establishment completion message to the current serving base station (S717). At this time, the terminal may integrity-protect the RRC resume or RRC re-establishment complete message through Krrc_int and encrypt it through Krrc_enc.

Meanwhile, the current serving base station may receive an RRC resume or RRC re-establishment complete message from the terminal. And, the current serving base station may transmit the terminal address indicator to the previous serving base station through the Xn-U interface (S718). Accordingly, the previous serving base station may receive a terminal address indicator from the current serving base station and may transmit SN (sequence number) state information to the current serving base station (S719). Here, the SN state is information indicating a progress state of a serial number for data in a packet data convergence protocol (PDCP) layer, and may be used for data encryption and integrity protection.

Meanwhile, the current serving base station may receive SN state information from the previous serving base station and may transmit a path change request message requesting a change of communication path from the previous serving base station to the current serving base station to the AMF (S720). Accordingly, the AMF may receive a path change request message from the current serving base station. And, the AMF can change the communication path of the terminal from the previous serving base station to the current serving base station. Thereafter, the AMF may transmit a route change request response message indicating that the route has been changed to the current serving base station (S721).

Accordingly, the current serving base station may receive a path change request response message from the AMF. Then, the current serving base station may transmit a context release message of the terminal requesting to release the context of the terminal to the previous serving base station (S722). Accordingly, the previous serving base station can receive the context release message of the terminal from the current serving base station. And, the previous serving base station may release the context of the terminal.

Through this process, the current serving base station can successfully perform the RRC resumption procedure or the RRC re-establishment procedure based on the context information of the terminal received from the previous serving base station. However, the current serving base station may apply an algorithm different from the security algorithm used by the previous serving base station to the RRC resume or RRC re-establishment message. At this time, the terminal may fail integrity verification for the received RRC resume or RRC re-establishment message. Alternatively, the UE may fail to decode the received RRC resume or RRC re-establishment message.

In order to examine this in more detail, it can be assumed that the terminal can support all SNOW3G, AES, and ZUC for security-related algorithms, and that the current serving base station and the previous serving base station determine the security algorithm by different decision-making logic. . In this situation, in the initial access, the terminal and the previous serving base station may establish a security context based on the SNOW3G algorithm according to the decision of the previous serving base station. Accordingly, at the time when the terminal transmits the RRC re-establishment request or RRC resume request message to the current serving base station, the algorithm used for the initial access to protect the integrity of the RRC re-establishment or RRC resume message expected to be received later is SNOW3G Based on , Kgnb* can be derived, and a subkey can be derived using the derived Kgnb*.

Meanwhile, the current serving base station may receive an RRC re-establishment request or an RRC resume request message from the terminal and transmit a context recovery request message of the terminal to the previous serving base station. In addition, the current serving base station may receive a context recovery response message of the terminal including security capability information indicating that the terminal can support all SNOW3G, AES, and ZUC from the previous serving base station. At this time, the current serving base station may use an AES security algorithm other than SNOW3G by an internal logic different from that of the previous serving base station. Accordingly, the local serving base station may derive the subkey Krrc_int using the AES security algorithm using Kgnb* included in the terminal's context recovery request message received from the previous serving base station.

In addition, the current serving base station may transmit an RRC re-establishment or RRC resume message to which integrity protection is applied to the terminal using Krrc_int derived through the AES security algorithm. At this time, the terminal may receive an RRC re-establishment or RRC resume message. At this time, since the terminal holds Krrc_int derived through the SNOW3G security algorithm through negotiation with the previous serving base station, the RRC message to which integrity protection is applied uses Krrc_int generated through the AES security algorithm received from the current serving base station. Integrity verification may fail. Accordingly, in the present application, a context recovery procedure of a terminal may be proposed using a new parameter capable of fundamentally preventing such a problem.

8 is a flowchart illustrating a second embodiment of a method for restoring a context of a terminal.

Referring to FIG. 8 , in a context recovery method of a terminal, a terminal may move from a communication area of a previous serving base station to a communication area of a current serving base station. At this time, the terminal may transmit an RRC resume or RRC re-establishment request message to the current serving base station (S811). At this time, the terminal may perform integrity protection on the RRC resume or RRC re-establishment request message using Krrc_int generated using the integrity security algorithm determined by the previous serving base station.

And, the encryption algorithm determined by the previous serving base station by the terminal may be, for example, SNOW3G. At this time, the terminal may perform encryption on the RRC resume or RRC re-establishment request message using Krrc_enc generated using an encryption algorithm determined by the previous serving base station. Here, the integrity security algorithm determined by the previous serving base station by the terminal may be, for example, SNOW3G. On the other hand, when the terminal transmits an RRC re-establishment request or an RRC resume request message to the current serving base station, the RRC expected to be received later Kgnb* may be derived based on AES, which is an algorithm used for initial access to protect the integrity of a re-establishment or RRC resume message, and a subkey Krrc_int may be derived using the derived Kgnb*.

In addition, the terminal is an algorithm used for initial access to decode an RRC re-establishment or RRC resume message that is expected to be received later at the time of transmitting the RRC re-establishment request or RRC resume request message to the current serving base station, for example. Kgnb* can be derived based on SNOW3G, and subkey Krrc_enc can be derived using the derived Kgnb*.

Meanwhile, the current serving base station may receive an RRC resume or RRC re-establishment request message from the terminal. And, the current serving base station may attempt to identify which context among the contexts being managed internally through a procedure for identifying the terminal, but may fail to identify the terminal (S812). Accordingly, the current serving base station may fail to recover the context of the terminal. In this case, the current serving base station may transmit a context retrieve request message of the terminal including the resume MAC-I or shortened MAC-I to the previous serving base station (S813). Accordingly, the previous serving base station may receive the context recovery request message of the terminal from the current serving base station.

And, the previous serving base station can identify the existing terminal from the resume MAC-I or shortened MAC-I included in the context recovery request message of the received terminal (S814). Then, the previous serving base station may transmit a context retrieve response message of the terminal including the context information of the terminal to the current serving base station (S815). At this time, the context recovery response message of the terminal may include the following parameters.

1) UE security capabilities: list of security-related algorithms supported by the UE

2) AS (autonomous system) security information: Kgnb derived from Kgnb*

3) Current security algorithm information: Information on the security algorithm set through the security settings of the previous serving base station and terminal

As such, the previous serving base station may additionally provide current security algorithm information to the context recovery response message of the terminal transmitted to the current serving base station, unlike the prior art. Parameters used at this time may be generally as shown in Table 1 below.

currentSecurityAlgoritym
{
integrityProtectioinAlgo ENUMERATED {SNOW3G, AES, ZUC},
encryptionAlgo ENUMERATED {SNOW3G, AES, ZUC}
}

Here, "integrityProtectioinAlgo ENUMERATED {SNOW3G, AES, ZUC}" may inform that any one of SNOW3G, AES, and ZUC can be selected and used as a security algorithm for integrity protection established between the previous serving base station and the terminal. And, "encryptionAlgo ENUMERATED{SNOW3G, AES, ZUC}" is a security algorithm for encryption set between the previous serving base station and the terminal, and can inform that any one of SNOW3G, AES, and ZUC can be selected and used. Unlike this, the previous If the security algorithm for integrity protection established between the previous serving base station and the terminal is, for example, AES, the serving base station may inform that AES is used as the current serving base station by setting the parameter to "currentSecurityAlgorithm.integrityProtectionAlgo=AES". In addition, if the encryption security algorithm set between the previous serving base station and the terminal is, for example, SNOW3G, the previous serving base station may set the parameter to "currentSecurityAlgorithm.encryptionAlgo=SNOW3G" to inform that SNOW3G is used as the current serving base station.

Meanwhile, the current serving base station may receive the context recovery response message of the terminal from the previous serving base station. Accordingly, the current serving base station can restore the context of the terminal based on the context information of the terminal in the context recovery response message of the terminal received from the previous serving base station. In addition, the current serving base station can know that the terminal can support all SNOW3G, AES, and ZUC through the terminal security capability information included in the context recovery response message of the terminal received from the previous serving base station.

In addition, the current serving base station can know the security algorithm that the terminal is currently using by setting with the previous serving base station through currently used security algorithm information included in the context recovery response message of the terminal received from the previous serving base station. For example, the integrity protection algorithm in the currently used security algorithm information may be AES.

Meanwhile, the current serving base station may derive Kgnb* by updating Kgnb, and may derive a subkey Krrc_int from Kgnb* through an integrity protection algorithm. In this case, the current serving base station may use a security algorithm different from that used by the previous serving base station for the terminal by internal logic different from that of the previous serving base station. For example, the current serving base station may use the ZUC security algorithm instead of the AES used by the previous serving base station as an integrity protection algorithm.

Accordingly, the local serving base station may derive the subkey Krrc_int using the ZUC security algorithm using Kgnb* included in the context recovery request message of the terminal received from the previous serving base station. And, as an example, the encryption algorithm in the currently used security algorithm information may be SNOW3G. Meanwhile, the current serving base station may derive Kgnb* by updating Kgnb, and may derive a subkey Krrc_enc from Kgnb* through an encryption algorithm.

In this case, the current serving base station may use a security algorithm different from that used by the previous serving base station for the terminal by internal logic different from that of the previous serving base station. For example, the current serving base station may use the ZUC security algorithm instead of SNOW3G used as an encryption algorithm by the previous serving base station. Accordingly, the local serving base station can derive the subkey Krrc_enc using the ZUC security algorithm using Kgnb* included in the terminal's context recovery request message received from the previous serving base station.

Thereafter, the current serving base station may transmit an RRC resume or RRC re-establishment message to the terminal (S716). The current serving base station can protect the integrity of the RRC resume or RRC re-establishment message through Krrc_int newly derived from Kgnb*. At this time, the current serving base station may transmit an RRC re-establishment or RRC resume message to which integrity protection is applied to the terminal using, for example, Krrc_int derived through the ZUC security algorithm.

In addition, the current serving base station may encrypt and transmit an RRC resume or RRC re-establishment message through Krrc_enc newly derived from Kgnb*. In this way, when the security algorithm used by the current serving base station and the security algorithm used by the previous serving base station are changed differently, the current serving base station changes the security algorithm to the terminal through an RRC resume or RRC re-establishment message (ie, a new security algorithm) can notify.

Notification of such a changed security algorithm can be achieved when the current serving base station transmits an RRC resume or RRC re-establishment message including information about a new security algorithm that has been changed. That is, the current serving base station may add a parameter shown in Table 2 below indicating new security algorithm information to the RRC resume or RRC re-establishment message.

newSecurityAlgoritym
{
integrityProtectioinAlgo ENUMERATED {SNOW3G, AES, ZUC},
encryptionAlgo ENUMERATED {SNOW3G, AES, ZUC}
}

Here, "integrityProtectioinAlgo ENUMERATED {SNOW3G, AES, ZUC}" is a security algorithm currently used by the serving base station for integrity protection, and may be SNOW3G, AES, or ZUC, and may indicate that any one of them can be selected and used. there is. In addition, "encryptionAlgo ENUMERATED {SNOW3G, AES, ZUC}" is a security algorithm currently used by the serving base station for encryption, and may be SNOW3G, AES, or ZUC, and may indicate that any one of them can be selected and used. Unlike this, the current serving base station may notify that the terminal has used ZUC by setting the parameter to “newSecurityAlgorithm.integrityProtectionAlgo=ZUC” when the set security algorithm for integrity protection is, for example, ZUC. In addition, if the current serving base station is, for example, ZUC, the set encryption security algorithm, it can set the parameter to “newSecurityAlgorithm.encryptionAlgo=ZUC” to inform the terminal that ZUC has been used.

Meanwhile, the terminal may receive an RRC resume or RRC re-establishment message from the current serving base station. At this time, the terminal can check new security algorithm information in the RRC resume or RRC re-establishment message, and according to the checked new security algorithm information, it can be confirmed that the security algorithm used by the current serving base station is different from the security algorithm used by the previous serving base station. can

Accordingly, the terminal may derive Kgnb* by updating Kgnb, and may derive Krrc_int from Kgnb* by using a security algorithm (eg, ZUC) according to new security algorithm information. In addition, the terminal may verify the integrity of the RRC resume or RRC re-establishment message through Krrc_int derived using a security algorithm (eg, ZUC) according to the new security algorithm information.

Meanwhile, the terminal may derive Kgnb* by updating Kgnb, and may derive Krrc_enc by using an encryption security algorithm (eg, ZUC) according to new security algorithm information from Kgnb*. And, the terminal may decode the RRC resume or RRC re-establishment message using the derived Krrc_enc.

Thereafter, the terminal may transmit an RRC resume or RRC re-establishment complete message to the current serving base station (S817). At this time, the terminal may integrity-protect the RRC resume or RRC re-establishment complete message through Krrc_int using a security algorithm according to new security algorithm information, and may encrypt it through Krrc_enc.

Meanwhile, the current serving base station may receive an RRC resume or RRC re-establishment complete message from the terminal. And, the current serving base station may transmit the terminal address indicator to the previous serving base station through the Xn-U interface (S818). Accordingly, the previous serving base station may receive a terminal address indicator from the current serving base station and may transmit SN status information to the current serving base station (S819). Here, the SN status is information indicating the progress status of serial numbers for data in the PDCP layer, and can be used for data encryption and integrity protection.

Meanwhile, the current serving base station may receive SN state information from the previous serving base station and may transmit a path change request message requesting a change of communication path from the previous serving base station to the current serving base station to the AMF (S820). Accordingly, the AMF may receive a path change request message from the current serving base station. And, the AMF can change the communication path of the terminal from the previous serving base station to the current serving base station. Thereafter, the AMF may transmit a route change request response message indicating that the route has been changed to the current serving base station (S821).

Accordingly, the current serving base station may receive a path change request response message from the AMF. Then, the current serving base station may transmit a context release message of the terminal requesting to release the context of the terminal to the previous serving base station (S822). Accordingly, the previous serving base station can receive the context release message of the terminal from the current serving base station. And, the previous serving base station may release the context of the terminal.

The methods according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded on a computer readable medium. Computer readable media may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on a computer readable medium may be specially designed and configured for the present invention or may be known and usable to those skilled in computer software. Examples of computer readable media may include hardware devices specially configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions may include not only machine language codes generated by a compiler but also high-level language codes that can be executed by a computer using an interpreter and the like. The hardware device described above may be configured to operate with at least one software module to perform the operations of the present invention, and vice versa. In addition, the above-described method or device may be implemented by combining all or some of its components or functions, or may be implemented separately.

Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention within the scope not departing from the spirit and scope of the present invention described in the claims below. You will understand that it can be done.

Claims (1)

As an operating method performed in a current serving base station of a communication system,
Receiving a radio resource control (RRC) request message from a terminal;
Requesting context recovery to a previous serving base station when identification of the terminal fails;
Receiving context information about the terminal and security algorithm information set with the terminal from the previous serving base station; and
Transmitting an RRC response message including security algorithm information in use to the terminal when the security algorithm according to the security algorithm information is different from the security algorithm in use, operating method performed in the current serving base station.

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